Phenology of a Lizard Assemblage in the Dry Chaco of Argentina

Individual species' phenologies can play an important role in the structure of lizard assem- blages over short time scales. Data from a pitfall study carried out in the dry Chaco of Argentina were used to address the question of how species are distributed in their assemblage through time. Lizard activity and species richness were highest in the spring breeding season and declined in the cool months of the year. Variations in seasonal activity patterns and reproductive chronology resulted in significantly different dis- tributions of species in every sample month. Not only did the species composition of the assemblage change through time, but the mean size of lizards and the proportions of males, females, and juveniles varied significantly for several species. Large lizards, regardless of species, disappeared from the assemblage during the cool, dry winter, while juveniles of the large species remained active year round. Adults of the smallest species were also active throughout the year. We propose an hypothesis based on thermoregulatory con- straints of lizard body size to account for these patterns. An approach focusing on the energetics and phys- iological ecology of individual species would be fruitful in understanding the dynamics of fluctuating lizard communities.